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This work investigates the very low frequency (VLF) modulation of QRS slopes and heart rate variability (HRV). Electrocardiogram (ECG) and respiratory flow signal were acquired from patients with dilated cardiomyopathy and ischemic cardiomyopathy. HRV as well as the upward QRS slope (IUS) and downward QRS slope (IDS) were extracted from the ECG. The relation between HRV and QRS slopes in the VLF band was measured using ordinary coherence in 5-minute segments. Partial coherence was then used to remove the influence that respiration simultaneously exerts on HRV and QRS slopes. A statistical threshold was determined, below which coherence values were considered not to represent a linear relation. 7 out of 276 segments belonging to 5 out of 29 patients for IUS and 10 segments belonging to 5 patients for IDS presented a VLF modulation in QRS slopes, HRV and respiration. In these segments spectral coherence was statistically significant, while partial coherence decreased, indicating that the coupling HRV and QRS slopes was related to respiration. 4 segments had a partial coherence value below the threshold for IUS, 3 segments for IDS. The rest of the segments also presented a notable decrease in partial coherence, but still above the threshold, which means that other non-linearly effects may also affect this modulation. [ABSTRACT FROM PUBLISHER]

Head down bed rest as Earth-based study for simulating microgravity affects cardiovascular system. However the consequences for the health of this experiment during and at recovery are still under research and in particular ventricular repolarization (VR) effects are not well known. VR dysfunctions could lead to cardiac arrhythmias and eventually to sudden cardiac death. Interactions of VR variability with heart rate variability (HRV) was used as proarrhythmic marker. In this study, three VR beat-to-beat indices extracted from ECG signals as QT, QTp (QRS on-set to T wave peak) and Tpe (peak to end of T wave) were measured and their variabilities studied. ARARX modeling was the tool used to estimate the VR variability fraction driven by HRV at different time periods: PRE, during head down bed rest (5-day & 21-day periods) and POST. We found significant differences (p-values < 0.01) comparing the repolarization variability content driven by heart rate in all VR series at PRE versus during BR microgravity conditions and after in both cases of study. Head down bed rest test increases the amount of linear dependency of VR variability and HRV. Results tend to evidence a slow recovery capacity for all VR variability after simulated microgravity exposition, being more notable for 21-day HDBR. [ABSTRACT FROM PUBLISHER]

The study of QT/RR relationship is important for the clinical evaluation of possible risk of ventricular tachyarrhythmia. Our aim was to assess the effects of 5-days of head-down (−6 degrees) bed-rest (HDBR) on ventricular repolarization. High fidelity 12-leads Holter ECG was acquired before (PRE), the last day of HDBR (HDT5), and five days after its conclusion (POST). X, Y, Z leads were derived (inverse Dower matrix) and vectorcardiogram computed. Selective beat averaging applied to the night period resulted in averages preceded by the same stable heart rate (for each 10 msec bin amplitude, in the range 900–1200 msec). For each template (i.e., one for each bin), T-wave maximum amplitude (Tmax), T wave area, R-Tapex and R-Tend were computed. Results (in 8 male volunteers) showed that, compared to PRE, at HDT5 both R-Tapex and R-Tend resulted significantly shortened (−5% and −3%, respectively), together with a decrease in T-wave area (−7%), while Tmax was unchanged. At POST, duration parameters showed a trend towards their control values (−1.5% and −3%, respectively) while amplitude parameters resulted restored. Despite the short-term BR, cardiac adaptation to deconditioning affected ventricular repolarization during the night period. [ABSTRACT FROM PUBLISHER]

T-wave alternans (TWA) has been linked to increased vulnerability of the myocardium to ventricular fibrillation in different clinical conditions. Our aim in this work was to study and characterize TWA in an animal model of myocardial ischemia and infarction. Infarction was induced in 29 pigs by a 40-minute-long balloon inflation on the left anterior descending coronary artery. The occlusion recording, as well as a previous baseline recordings were analyzed using the Laplacian Likelihood Method together with Periodic Component Analysis. TWA was found in 27 occlusion recordings and in only 4 baseline recordings. A two/three-peaked pattern was commonly found in the time-course of TWA, where the first peak of TWA was attained at 5 to 7 minutes from the onset of occlusion and the second at about 15 to 20 minutes. After 24 min of occlusion TWA had faded in most recordings. Analysis of the TWA amplitude lead distribution revealed that maximum TWA appears in leads V3 and V4, in consonance with human studies, confirming the regional nature of ischemia-induced TWA. [ABSTRACT FROM PUBLISHER]

In this study, alterations in the cardiovascular system caused by ventricular premature beats (VPBs) are investigated by analyzing the photoplethysmographic (PPG) signal. A simple algorithm for PPG-based detection of VPBs is devised and evaluated, and then employed for the analysis of heart rate turbulence (HRT), here labelled “pulse rate turbulence” (PRT). The pulse transit time is also studied as it constitutes the main difference between HRT and PRT. The data sets included a total of 3872 VPBs and 13169 normal beats. The results showed that VPBs can be detected from the PPG signal with a sensitivity of 92.8%, a specificity of 99.8% and an accuracy of 99.3%, using six features and a simple linear classifier. The shape of PRT was found to resemble that of HRT, the latter type of turbulence resulting from ECG-based analysis, suggesting that PRT analysis can be used as a replacement for HRT analysis when the ECG is not available. [ABSTRACT FROM PUBLISHER]

T-wave alternans (TWA) is considered as an index of susceptibility of sudden cardiac death (SCD). The utility of TWA testing during ambulatory monitoring is being increasingly studied. A common approach for ambulatory TWA testing is to quantify the maximum amplitude of TWA in an ECG record, which requires visual verification of the results to discard erroneous measurements due to noise or artifacts in the ECG. This work presents a fully-automated method to quantify the average TWA activity in ambulatory ECGs. Our results indicate that quantifying the average TWA activity instead of the maximum TWA amplitude allows the prediction of SCD in in patients with chronic heart failure (CHF). [ABSTRACT FROM PUBLISHER]

Acute hypotensive episodes are common during dialysis sessions, and represent a serious problem. Spectral analysis of heart rate variability (HRV) and barorrefle x sensitivity (BRS) is performed to study the behaviour of the autonomic nervous system (ANS) during the hemodialysis. The ratio between the low frequency (LF) and high frequency (HF) power of HRV, as well as BRS in the HF band, are significantly different in patients being prone and resistant to hypotension (p<0.001 and p<0.05, respectively). Moreover, a very low frequency (VLF) modulation visible in HRV, blood pressure and the series of rotation angles of the heart's electrical axis have been studied. It turns out that the VLF component is more pronounced and with higher coherence in prone patients (p<0.05), suggesting a possible relation with altered or imbalanced ANS regulation. [ABSTRACT FROM PUBLISHER]

In this work, a comparative study of several electrogram (EGM) organization and synchronization indices in atrial fibrillation (AF) has been performed. To do this, a realistic EGM simulator has been designed. In order to see how the indices are affected by noise and local activation time and conduction variability, the signal-to-noise ratio (SNR), the delay between leads and its variability have been modified in a controlled way. With these different signals, several EGM risk indices (based on spectral, cross-covariance, information and wavefront analysis) have been calculated. Results suggest that indices based on spectral and cross-covariance analysis (organization index, spectral coherence and maximum normalized cross-covariance) are more robust than those based on wavefront or cross-information in quantifying the organization, synchronization and delay when SNR is reduced. [ABSTRACT FROM PUBLISHER]

There are evidences suggesting that spaceflight may be associated with increased susceptibility to ventricular dysrhythmias. To explore this hypothesis, five days −6° head-down bed rest (HDBR) was performed with the aim at testing the changes in QT/RR dynamics. Electrocardiogram signals (ECG) was acquired in 22 males during tilt-tests performed before and after HDBR. The dynamics of QT interval adaptation in response to upward and downward heart rate (HR) changes during the tilt test was evaluated modeling QT dependence on a history of previous RR intervals. The adaptation time of QT to abrupt changes in RR (t90) was found reduced after HDBR, with no changes in the optimum regression residuum (ropt) of the QT/RR dynamics. However, a dependence of the results to the width of the memory window considered was found. HDBR seems to induce variations in the phenomena by shortening the memory lag in QT/RR dependecy. [ABSTRACT FROM PUBLISHER]